The present invention relates in general to electrode holders and in particular to a new and useful electrode holder, particularly for smelting furnaces, which includes a clamping jaw opening device having all components positioned within an electrode arm of the electrode holder.
Electric smelting furnaces are supplied with electric power through high-amperage cables and conductor tubes of copper which are secured to water-cooled electrode arms movable in a vertical plane and connected to fixed contact jaws of water-cooled electrode holders which are provided on a front face of the electrode arms. To minimize the contact resistance between the graphite electrode and the mating contact surface of the contact jaw, a clamping jaw is provided in the electrode holder opposite the contact jaw, by which the electrode is firmly pressed into contact and held in place. The contact pressure is produced by a pretensioned spring and transmitted through levers or a linkage to the electrode holder.
To insert the graphite electrode into the electrode holder, or if a displacement of the electrode is necessary, the spring force acting on the clamping jaw is removed and, by enlarging the inside diameter of the electrode holder, the holder is disengaged from the graphite electrode. The contact pressure is removed by means of a pneumatic or hydraulic cylinder whose piston, upon being supplied with the pressure fluid, causes compression of the spring and displacement of the clamping mechanism of the electrode holder in the "opening" direction. Upon inserting or displacing the electrode, the fluid pressure is removed and the spring force again provides for a secure contact pressure and fixing of the electrode in the electrode holder.
In prior art electric furnaces, the mechanism for clamping and opening is mounted outside the electrode arm (see German Pat. No. 847,319 which is here incorporated by reference). It was also provided to dispose the clamping spring within the electrode arm (German Pat. No. 946,303 also incorporated by reference). A hydraulically operated cylinder for removing the contact pressure has the advantage over a pneumatically operated one that it is of smaller size. The pressure fluid is supplied into a hydraulic or pneumatic cylinder through flexible pressure tubes which are connected to the respective supply unit on the furnace floor.
The mentioned installations have the disadvantage that they are not protected against the hot atmosphere developing above the furnace, nor against the magnetic fields of the power supply to the furnace, and particularly that the flexible tubes supplying the operating fluid, whose length must correspond to the range of displacement of the electrode arm, are subjected to high mechanical stresses and therefore, may cause considerable trouble in operation and even accidents. Especially if hydraulic oil is used as the operating fluid, leakage at defective locations increases the fire hazard.